The present invention relates generally to window films including a metal layer and, more particularly, to a method of imparting corrosion resistance to the edge of such window films.
Window films are commonly used in commercial buildings, residential homes, and in automotive applications to save energy, improve comfort, provide UV protection, prevent the leakage of high frequency communications signals from the structure, and help reduce the dangers associated with window breakage. Such window films are commercially available from 3M Company, St. Paul, Minn., under the Scotchtint window film product designation.
Such window films may include a metal layer, such as a vapor deposited layer of silver. High conductivity of the metal layer is desirable where the window film is to be used to prevent leakage of high frequency (e.g. 100 MHz-6 GHz) communication signals from the structure. In order to achieve a window film having the best combination of high conductivity, high transmission and high reflection, it is desirable to use pure silver for the metal layer.
Silver layers are highly prone to corrosion in the presence of atmospheric elements such as water and chlorine, particularly along the edges of the window film. That is, even through the layer of silver of a window film may be protected by a coating or a laminated film, the silver layer will be exposed to the corrosive elements of the surrounding environment along its edges. The corrosion process is accelerated with increased ambient temperature in the presence of salt and moisture. Corrosion is aesthetically undesirable and also interferes with the performance of the window film. To protect it from corrosion, the silver layer is often alloyed or sandwiched between layers of other metals, such as copper or gold. These corrosion protection methods, however, add cost to the window film, alter the appearance and optical transmission of the window film, and decrease the conductivity of the metal layer.
In many instances, a window film having low reflection in the visible part of the solar spectrum (400-800 nm) is desirable while maintaining a high degree of reflection in the near IR range (800 nm-2500 nm). Multi-layer window film constructions having a dielectric/metal/dielectric in an A/B/A/B . . . type sequence may be made by tailoring the thickness of the individual layers such that the reflection in the visible range is suppressed. Such films are described in, for example, U.S. Pat. Nos. 6,007,901 (Maschwitz, et al.) and 6,391,400 (Russell, et al.).
U.S. Pat. No. 4,645,714 (Roche) discloses durable, secularly reflective mirrors for solar reflectors or fluorescent lamp fixtures that are formed by vapour-depositing silver on a polyester film and protectively covering it with a coating of transparent acrylate polymer containing a silver corrosion inhibitor such as glycol dimercaptoacetate.
U.S. Pat. No. 6,090,451 (Barth et al.) discloses edge sealing a window film by moving a porous applicator tip saturated with liquid sealant in wiping contact along an edge of the window film to be sealed so as to transfer a portion of the liquid sealant from the saturated applicator tip to the window film edge.
U.S. Pat. No. 6,294,233 (Barth et al.) discloses transparent edge sealed window films. The edges of the window film are preferably sealed by a liquid solvated polymer material which, upon curing, provides a solid transparent seal which significantly minimizes the degradative effects of the ambient environment.
The need exists for a corrosion resistant window film and, more particularly, for a simple, inexpensive, and effective method of imparting corrosion resistance to an exposed edge portion of a metal layer, such as silver, of a multilayer window film, including existing window films that are commercially available.